install debug into DebugProxy

Author: samuelcolvin

devtools/__main__.py

@@ -7,17 +7,27 @@
 # language=python
 install_code = """
 # add devtools `debug` function to builtins
-import sys
-# we don't install here for pytest as it breaks pytest, it is
-# installed later by a pytest fixture
-if not sys.argv[0].endswith('pytest'):
-    import builtins
-    try:
-        from devtools import debug
-    except ImportError:
-        pass
-    else:
-        setattr(builtins, 'debug', debug)
+# we don't want to import devtools until it's required
+# since it breaks pytest, hence this proxy
+class DebugProxy:
+    def __init__(self):
+        self._debug = None
+
+    def _import_debug(self):
+        if self._debug is None:
+            from devtools import debug
+            self._debug = debug
+
+    def __call__(self, *args, **kwargs):
+        self._import_debug()
+        return self._debug(*args, **kwargs)
+
+    def __getattr__(self, item):
+        self._import_debug()
+        return getattr(self._debug, item)
+
+import builtins
+setattr(builtins, 'debug', DebugProxy())
 """
 
 
@@ -27,12 +37,6 @@ def print_code() -> int:
 
 
 def install() -> int:
-    print('[WARNING: this command is experimental, report issues at github.com/samuelcolvin/python-devtools]\n')
-
-    if hasattr(builtins, 'debug'):
-        print('Looks like devtools is already installed.')
-        return 0
-
     try:
         import sitecustomize  # type: ignore
     except ImportError:
@@ -48,7 +52,11 @@ def install() -> int:
     else:
         install_path = Path(sitecustomize.__file__)
 
-    print(f'Found path "{install_path}" to install devtools into __builtins__')
+    if hasattr(builtins, 'debug'):
+        print(f'Looks like devtools is already installed at `{install_path}`.')
+        return 0
+
+    print(f'Found path `{install_path}` to install devtools into __builtins__')
     print('To install devtools, run the following command:\n')
     print(f'    python -m devtools print-code >> {install_path}\n')
     if not install_path.is_relative_to(Path.home()):